PURPOSE: To prevent deformation of louvers during their forming process and make a smooth air flow by a method wherein some small projections made by a drawing work are provided in order to reduce a difference in developed lengths of each of louvers having a difference in steps.
CONSTITUTION: A planer surface of a corrugated fin 10 is provided with a repetition of alternative group of louvers with a predetermined stepped pattern of arrangement by some cut and raised louvers 2, 3, 4 and 5 except a part 1 of the plane and the cut and raise margin 1. A part of the fins 10 is contacted with a thermal conducting pipe 6. A drawing force is applied to an entire louver from both longitudinal sides of the louver toward its central part so as to form small projections 7 at the central part of the louver. Small projections 7 are provided in the louver having the shortest developing length under a drawing work, so that it is possible to reduce a difference in developed lengths during a drawing work at both louver 1 and the upper-most louver 2 having a large developed length. Even if the drawing force acting upon the upper-most louver 2 is influenced against the louver 1, this drawing force is adsorbed by the louver 1 so as to restrict any deformation of each of the louvers 1. An edge line of each of small projections 7 is arranged in parallel with an air flowing direction A, so that a smooth air flow can be held.
YUKITA HISASHI
SAWAHATA TAKATOMO
KUDO MITSUO
